Our previous studies have demonstrated that promoter-green fluorescent protein (GFP) transgenes can be used to identify and isolate populations of cells at the preosteoblastic stage (pOBCol3.6GFP) and at the mature osteoblastic stage (pOBCol2.3GFP) in living primary bone cell cultures. This strategy forms the basis for appreciating the cellular heterogeneity of lineage and relating gene function to cell differentiation. A weakness of this approach was the lack of a selective marker for late osteoblasts and mature osteocytes in the mineralized matrix. In this study, we have examined the expression of DMP-1 mRNA in murine marrow stromal and calvarial osteoblast cultures, and in bone, and calvaria in vivo. Furthermore, we have generated transgenic mice utilizing a mouse DMP1 cis-regulatory system to drive GFP as a marker for living osteocytes. Transgene expression was directed to mineralized tissues and showed a high correlation with the expression of the endogenous gene. Osteocyte-restricted expression of GFP was observed in histological sections of femur and calvaria and in primary cell cultures. Generation of this transgenic model will facilitate studies of gene expression and biological functions in these terminally differentiated bone cells.